Adenylyl cyclase has previously been localized in tissue slices utilizing autoradiographic analysis of slices that had been incubated with 3-H- forskolin. The use of the tritiated ligand required exposure times of up to four weeks. We have developed two different iodinated derivatives of forskolin that bind to adenylyl cyclase and the glucose transporter respectively with high affinity. The specificity of the ligands has been determined and experimental protocols can be used to demonstrate specific binding of one derivative, 6-IHPP-Fsk, to adenylyl cyclase, and another derivative, 7-IHPP-Fsk, to the glucose transporter. These ligands were used to localize adenylyl cyclase and the glucose transporter in rat brain slices. The binding sites associated with adenylyl cyclase or the glucose transporter required only 10-15 hours for optimal exposure. The distribution of adenylyl cyclase as assessed using 6-IHPP-Fsk was identical to that previously determined using 3-H-forskolin. In contrast, there was a marked difference between the distribution of the glucose transporter and adenylyl cyclase. These studies are now being extended in order to look at the localization of these binding sites during development and to determine effects of toxicity on adenylyl cyclase and the glucose transporter.